1. Field of the Invention
This invention relates to radio receivers and it has particular utility for multi-mode mobile phones but is not so limited.
2. Description of the Related Art
Most modem receivers are based on a conventional heterodyne topology. For a description of the prior art and technological background reference is made to the paper on xe2x80x9cRecent Advances in RF Integrated Circuitsxe2x80x9d by Behzad Razavi published in IEEE Communications Magazine, December 1997. U.S. Pat. No. 4,653,117 to Heck also discloses relevant prior art.
These conventional heterodyne receivers make use of a fixed IF and incorporate a narrow band IF filter designed to pass only the wanted signal and reject the large unwanted signals. The large unwanted signals, if not removed by the narrow band IF filter would otherwise compress/saturate the latter stages of the receiver, i.e., the demodulator and so reduce the sensitivity of the receiver. The IF filter is normally a SAW device and so cannot be integrated into a semiconductor process.
Receivers designed to operate with networks having different radio standards generally have different data bandwidths and so the IF filter bandwidth would need to be changed to accommodate operation with the different bandwidths. Under existing arrangements the changes in IF filter bandwidth needed for multi-mode radio would require a plurality of SAW filters.
The following abbreviations and terminology are used herein:
GSMxe2x80x94Global System for Mobile communications, (formerly Groupe Special Mobile)
SAWxe2x80x94Surface acoustic wave
LNAxe2x80x94Low noise amplifier
ASICxe2x80x94Application specific integrated circuit
IFxe2x80x94ntermediate frequency
RFxe2x80x94Radio frequency
MULTI-MODExe2x80x94This describes herein a capability to accommodate a number of different data bandwidths rather than different methods of multiple access. The receiver is not limited, however, to any particular multiple access method.
An object of the present invention is to provide a receiver with broadband IF and multi-mode capability which obviates the need for IF filters and can be implemented fully in ASIC. A further object of the invention is an improved multi-mode homodyne receiver. Further advantages anticipated for the invention are improved flexibility of frequency planning, reduction of the pass band group delay ripple normally associated with SAW filters and cost reduction through the elimination of SAW filters.
According to one aspect of the invention there is provided a heterodyne radio receiver, having a broadband IF, in which the outputs from the second down-conversion mixer of the receiver are high pass filtered to select unwanted signals and low pass filtered to select wanted signals, the unwanted signals being up-converted to IF in an up-conversion mixer, phase shifted and added in anti-phase to an input or inputs of the second down-conversion mixer.
According to a further aspect of the invention there is provided a homodyne radio receiver in which the outputs from the down-conversion mixer of the receiver are high pass filtered to select unwanted signals and low pass filtered to select wanted signals, the unwanted signals being up-converted to RF in an up-conversion mixer, phase shifted and added in anti-phase to an input or inputs of the down-conversion mixer.